1. Field of the Invention
The present invention relates to a developing device that forms an image using an electrophotographic system, and an image forming apparatus having the same.
2. Description of the Related Art
Conventionally, developing devices include those that use a two-component developer having non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. For example, in Japanese Patent Laid-Open No. 05-333691, the developing device using the two-component developer is generally configured as illustrated in FIG. 27. FIG. 27 is an explanatory view of a conventional developing device.
A conventional developing device 101 is equipped with a developing container 102 containing the developer, and has a developing sleeve 108 that is a developer carrier at an opening facing a photosensitive drum (not illustrated) that is an image bearing member. Thus, a developing chamber 103 and an agitating chamber 104 into which the developing container 102 is partitioned with a partition 107 are vertically formed in the developing container 102 at an opposite side of the opening. A conveying screw 105 and a conveying screw 106 are disposed in the developing chamber 103 and the agitating chamber 104, respectively. Through operations of the conveying screw 105 and the conveying screw 106, a developer and a toner in the developing chamber 103 and the agitating chamber 104 are agitated and conveyed, and a toner density in the developer is made uniform.
Further, a regulating blade 109 is disposed above the developing sleeve 108 as a layer thickness regulating member. The developer is uniformly coated on the developing sleeve 108 by the regulating blade 109, and is conveyed up to a developing region. A gap between the developing sleeve 108 and the regulating blade 109 is adjusted so that the developer is fed to the developing region in a uniform and steady way.
Here, to cause the developer to be more steadily fed to the developing region, the developer needs to be steadily fed to an upstream side of the regulating blade 109 based on a rotational direction of the developing sleeve 108. Accordingly, the inventors examined providing a guide member for securing the developer at a tip 107a of the partition 107 which is located at a side of the developing sleeve 108 and at a more upstream side than the regulating blade 109 based on the rotational direction of the developing sleeve 108.
However, if the guide member for securing the developer is provided at the upstream side of the regulating blade 109 based on the rotational direction of the developing sleeve 108, the developer may stick to a surface of the guide member, and the coating on the developing sleeve 108 may be made unsteady. This phenomenon tends to take place particularly when the developer is deteriorated.
The deterioration of the developer means that, due to a collision between the toner and the developing sleeve or between the toners, the toner and particularly a convex part of the toner is damaged, or an external additive on a toner surface is buried in the toner surface.
When the deterioration of the developer occurs, the external additive such as silica added to improve fluidity of the toner is buried in the toner surface. Thereby, an adhesive force of the toner is increased, and the fluidity is reduced. This developer deterioration is prone to take place mainly when an image with a low consumption of the toner continues to be output for a long time, because the developer is agitated inside the developing device for a long time.
Thus, if this developer deterioration takes place, the adhesive force of the toner is increased. As such, the friction against the surface of the guide member makes it easier for the developer to adhere. In this way, when the guide member and the developer adhere to each other, a region between the regulating blade 109 and the guide member is narrowed, and the developer cannot be steadily fed to a nap cutting portion of the regulating blade 109. As a result, problems such as the coating on the developing sleeve 108 failing to be uniform occur.
To solve the above problems, a configuration in which a distance between the regulating blade 109 and the guide member is increased is also taken into consideration. That is, a configuration in which an installed position of the guide member is set to be a more upstream side with respect to of the regulating blade 109 based on the rotational direction of the developing sleeve 108 is also taken into consideration.
However, as a distance between a lower end of the guide member and the regulating blade 109 is increased, the developer receiving an external force from the developing sleeve 108 is increased, and the developer deterioration is accelerated. For this reason, the lower end of the guide member approaches the side of the regulating blade 109. Therefore, the top of the guide member needs to be kept away from the regulating blade 109. Then, the guide member should be installed at a certain angle but not in a vertical direction.